The present invention relates to the separation of components from methanol mixtures thereof by extractive distillation.
Extractive distillation is a process to separate close-boiling compounds from each other by introducing a selectively-acting third component, the extractive distillation solvent, with the result that the relative volatility of the mixture to be separated is increased and azeotropes, if present, are overcome. The extractive distillation solvent is to be selected such that it does not form an undesired azeotrope with any of the compounds in the mixture.
The separation of methanol and acetone is complicated due to the existence of an azeotrope. Water or ethylene glycol have been proposed in the literature as extractive distillation solvents to produce methanol as distillate.
The separation of methanol and methyl acetate is complicated due to the existence of an azeotrope. 2-Methoxy ethanol has been proposed in the literature as extractive distillation solvents to produce methyl acetate as distillate.
As has been stated in U.S. Pat. No. 5,800,681 (Berg) extractive distillation is the method of separating close boiling compounds from each other by carrying out the distillation in a multiplate rectification column in the presence of an added liquid or liquid mixture, said liquid(s) having a boiling point higher than the compounds being separated. The extractive distillation solvent is introduced near the top of the column and flows downward until it reaches the stillpot or reboiler. Its presence on each plate of the rectification column alters the relative volatility of the close boiling compounds in a direction to make the separation on each plate greater and thus require either fewer plates to effect the same separation or make possible a greater degree of separation with the same number of plates. The extractive distillation solvent should boil higher than any of the close boiling liquids being separated and not form minimum azeotropes with them. Usually the extractive distillation solvent is introduced a few plates from the top of the column to ensure that none of the extractive distillation solvent is carried over with the lowest boiling component.
It is an object of this invention to suggest at least one further extractive distillation solvent for the separation of components from mixtures thereof.
According to the invention, a method of separation of methanol from a mixture of methanol and another compound selected from a first group consisting of acetone and methyl acetate, includes the step of distilling the mixture containing at least methanol and another compound selected from a first group consisting of acetone and methyl acetate by way of an extractive distillaton process in the presence of an extractive distillation solvent selected from a second group consisting of a secondary amine, a chlorinated hydrocarbon, a brominated hydrocarbon, a paraffin, an amine, a halogenated hydrocarbon, an alkylated thiopene and a diol.
The mixture may contain methanol and acetone and the extractive distillation solvent may be selected from a group consisting of a secondary amine, a chlorinated hydrocarbon, a brominated hydrocarbon and a paraffin.
The methanol and acetone mixture may contain only methanol and acetone.
The secondary amine may be selected from a group consisting of N,Nxe2x80x2-dimethyl-1,3-propanediamine, N,Nxe2x80x2-dimethylethylenediamine and dibutylamine.
The chlorinated hydrocarbon may be selected from a group consisting of hexachlorobutadiene and tetrachloroethylene.
The brominated hydrocarbon may be 1,4-dibromo-butane.
The paraffin may be at least one of the components selected from a group consisting of undecane, dodecane, tridecane and tetradecane.
The mixture may contain methanol and methyl acetate and the extractive distillation solvent may be selected from a group consisting of an amine, a halogenated hydrocarbon, an alkylated thiopene, a diol and a paraffin.
The methanol and methyl acetate mixture may contain only methanol and methyl acetate.
The amine may be selected from a group consisting of N,Nxe2x80x2-dimethylethylenediamine, N,Nxe2x80x2-dimethyl-1,3-propanediamine, diethylenetriamine, hexamethylenediamine, 1,4-diaminobutane and 1,3-diaminopentane.
The halogenated hydrocarbon may be selected from a group consisting of hexachlorobutadiene, tetrachloroethylene and dibromobutane.
The alkylated thiopene may be ethyl thiopene.
The diol may be diethylene glycol.
The paraffin may be at least one of the components selected from a group consisting of undecane, dodecane, tridecane and tetradecane.